For some reason, I get 1.797693134862316e+308 as an empty value in iFractals() instead of 0.
Is it a bug or is it a normal behavior?
It's normal planned behavior. You got DBL_MAX - see section Numerical Type Constants.
The built EMPTY_VALUE constant equals this value. See also sample in the Methods of Object Binding section, there is using of comparison iFractals indicator values to EMPTY_VALUE.